(**
 * Copyright (c) 2013-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *)

module Ast = Flow_ast

open Flow_ast_visitor
open Hoister

module Make
    (L: Loc_sig.S)
    (Api: Scope_api_sig.S with module L = L)
    : Scope_builder_sig.S with module L = L and module Api = Api
= struct
  module L = L
  module Api = Api

  open Api
  class with_or_eval_visitor = object(this)
    inherit [bool, L.t] visitor ~init:false as super

    method! expression (expr: (L.t, L.t) Ast.Expression.t) =
      let open Ast.Expression in
      if this#acc = true then expr else match expr with
      | (_, Call { Call.callee = (_, Identifier (_, "eval")); _}) ->
        this#set_acc true;
        expr
      | _ -> super#expression expr

    method! statement (stmt: (L.t, L.t) Ast.Statement.t) =
      if this#acc = true then stmt else super#statement stmt

    method! with_ _loc (stuff: (L.t, L.t) Ast.Statement.With.t) =
      this#set_acc true;
      stuff
  end

  (* Visitor class that prepares use-def info, hoisting bindings one scope at a
     time. This info can be used for various purposes, e.g. variable renaming.

     We do not generate the scope tree for the entire program, because it is not
     clear where to hang scopes for function expressions, catch clauses,
     etc. One possibility is to augment the AST with scope identifiers.

     As we move into a nested scope, we generate bindings for the new scope, map
     the bindings to names generated by a factory, and augment the existing
     environment with this map before visiting the nested scope.
  *)
  module Acc = struct
    type t = info
    let init = {
      max_distinct = 0;
      scopes = IMap.empty;
    }
  end

  module Env : sig
    type t
    val empty: t
    val mk_env: (unit -> int) -> t -> L.t Bindings.t -> t
    val get: string -> t -> Def.t option
    val defs: t -> Def.t SMap.t
  end = struct
    type t = Def.t SMap.t list
    let empty = []

    let rec get x t =
      match t with
      | [] -> None
      | hd::rest ->
        begin match SMap.get x hd with
        | Some def -> Some def
        | None -> get x rest
        end

    let defs = function
      | [] -> SMap.empty
      | hd::_ -> hd

    let mk_env next parent_env bindings =
      let bindings = Bindings.to_assoc bindings in
      let env = List.fold_left (fun env (x, locs) ->
        let name = match get x parent_env with
          | Some def -> def.Def.name
          | None -> next () in
        SMap.add x { Def.locs; name; actual_name=x } env
      ) SMap.empty bindings in
      env::parent_env
  end

  class scope_builder = object(this)
    inherit [Acc.t, L.t] visitor ~init:Acc.init as super

    val mutable env = Env.empty
    val mutable current_scope_opt = None
    val mutable scope_counter = 0
    val mutable uses = []

    method private new_scope =
      let new_scope = scope_counter in
      scope_counter <- scope_counter + 1;
      new_scope

    val mutable counter = 0
    method private next =
      let result = counter in
      counter <- counter + 1;
      this#update_acc (fun acc -> { acc with
        max_distinct = max counter acc.max_distinct
      });
      result

    method with_bindings: 'a. ?lexical:bool -> L.t -> L.t Bindings.t -> ('a -> 'a) -> 'a -> 'a =
      fun ?(lexical=false) loc bindings visit node ->
        let save_counter = counter in
        let save_uses = uses in
        let old_env = env in
        let parent = current_scope_opt in
        let child = this#new_scope in
        uses <- [];
        current_scope_opt <- Some child;
        env <- Env.mk_env (fun () -> this#next) old_env bindings;
        let result = Core_result.try_with (fun () -> visit node) in
        this#update_acc (fun acc ->
          let defs = Env.defs env in
          let locals = SMap.fold (fun _ def locals ->
            Nel.fold_left (fun locals loc -> L.LMap.add loc def locals) locals def.Def.locs
          ) defs L.LMap.empty in
          let locals, globals = List.fold_left (fun (locals, globals) (loc, x) ->
            match Env.get x env with
            | Some def -> L.LMap.add loc def locals, globals
            | None -> locals, SSet.add x globals
          ) (locals, SSet.empty) uses in
          let scopes = IMap.add child { Scope.lexical; parent; defs; locals; globals; loc; } acc.scopes in
          { acc with scopes }
        );
        uses <- save_uses;
        current_scope_opt <- parent;
        env <- old_env;
        counter <- save_counter;
        Core_result.ok_exn result

    method! identifier (expr: L.t Ast.Identifier.t) =
      uses <- expr::uses;
      expr

    method! jsx_identifier (id: L.t Ast.JSX.Identifier.t) =
      let open Ast.JSX.Identifier in
      let loc, {name} = id in
      uses <- (loc, name)::uses;
      id

    (* don't rename the `foo` in `x.foo` *)
    method! member_property_identifier (id: L.t Ast.Identifier.t) = id

    (* don't rename the `foo` in `const {foo: bar} = x` *)
    method! pattern_object_property_identifier_key ?kind id = ignore kind; id

    (* don't rename the `foo` in `{ foo: ... }` *)
    method! object_key_identifier (id: L.t Ast.Identifier.t) = id

    method! block loc (stmt: (L.t, L.t) Ast.Statement.Block.t) =
      let lexical_hoist = new lexical_hoister in
      let lexical_bindings = lexical_hoist#eval (lexical_hoist#block loc) stmt in
      this#with_bindings ~lexical:true loc lexical_bindings (super#block loc) stmt

    (* like block *)
    method! program (program: (L.t, L.t) Ast.program) =
      let loc, _, _ = program in
      let lexical_hoist = new lexical_hoister in
      let lexical_bindings = lexical_hoist#eval lexical_hoist#program program in
      this#with_bindings ~lexical:true loc lexical_bindings super#program program

    method private scoped_for_in_statement loc (stmt: (L.t, L.t) Ast.Statement.ForIn.t) =
      super#for_in_statement loc stmt

    method! for_in_statement loc (stmt: (L.t, L.t) Ast.Statement.ForIn.t) =
      let open Ast.Statement.ForIn in
      let { left; right = _; body = _; each = _ } = stmt in

      let lexical_hoist = new lexical_hoister in
      let lexical_bindings = match left with
      | LeftDeclaration (loc, decl) ->
        lexical_hoist#eval (lexical_hoist#variable_declaration loc) decl
      | LeftPattern _ -> Bindings.empty
      in
      this#with_bindings ~lexical:true loc lexical_bindings (this#scoped_for_in_statement loc) stmt

    method private scoped_for_of_statement loc (stmt: (L.t, L.t) Ast.Statement.ForOf.t) =
      super#for_of_statement loc stmt

    method! for_of_statement loc (stmt: (L.t, L.t) Ast.Statement.ForOf.t) =
      let open Ast.Statement.ForOf in
      let { left; right = _; body = _; async = _ } = stmt in

      let lexical_hoist = new lexical_hoister in
      let lexical_bindings = match left with
      | LeftDeclaration (loc, decl) ->
        lexical_hoist#eval (lexical_hoist#variable_declaration loc) decl
      | LeftPattern _ -> Bindings.empty
      in
      this#with_bindings ~lexical:true loc lexical_bindings (this#scoped_for_of_statement loc) stmt

    method private scoped_for_statement loc (stmt: (L.t, L.t) Ast.Statement.For.t) =
      super#for_statement loc stmt

    method! for_statement loc (stmt: (L.t, L.t) Ast.Statement.For.t) =
      let open Ast.Statement.For in
      let { init; test = _; update = _; body = _ } = stmt in

      let lexical_hoist = new lexical_hoister in
      let lexical_bindings = match init with
      | Some (InitDeclaration (loc, decl)) ->
        lexical_hoist#eval (lexical_hoist#variable_declaration loc) decl
      | _ -> Bindings.empty
      in
      this#with_bindings ~lexical:true loc lexical_bindings (this#scoped_for_statement loc) stmt

    method! catch_clause loc (clause: (L.t, L.t) Ast.Statement.Try.CatchClause.t') =
      let open Ast.Statement.Try.CatchClause in
      let { param; body = _ } = clause in

      (* hoisting *)
      let lexical_bindings = match param with
        | Some p ->
          let lexical_hoist = new lexical_hoister in
          lexical_hoist#eval lexical_hoist#catch_clause_pattern p
        | None -> Bindings.empty
        in
      this#with_bindings ~lexical:true loc lexical_bindings (super#catch_clause loc) clause

    (* helper for function params and body *)
    method private lambda loc params body =
      (* function params and bindings within the function body share the same scope *)
      let bindings =
        let hoist = new hoister in
        run hoist#function_params params;
        run hoist#function_body_any body;
        hoist#acc
      in

      this#with_bindings loc bindings (fun () ->
        run this#function_params params;
        run this#function_body_any body;
      ) ()

    method! function_declaration loc (expr: (L.t, L.t) Ast.Function.t) =
      let contains_with_or_eval =
        let visit = new with_or_eval_visitor in
        visit#eval (visit#function_declaration loc) expr
      in

      if not contains_with_or_eval then begin
        let open Ast.Function in
        let {
          id; params; body; async = _; generator = _;
          predicate = _; return = _; tparams = _;
        } = expr in

        run_opt this#function_identifier id;

        this#lambda loc params body;
      end;

      expr

    (* Almost the same as function_declaration, except that the name of the
       function expression is locally in scope. *)
    method! function_ loc (expr: (L.t, L.t) Ast.Function.t) =
      let contains_with_or_eval =
        let visit = new with_or_eval_visitor in
        visit#eval (visit#function_ loc) expr
      in

      if not contains_with_or_eval then begin
        let open Ast.Function in
        let {
          id; params; body; async = _; generator = _;
          predicate = _; return = _; tparams = _;
        } = expr in

        let bindings = match id with
          | Some name -> Bindings.singleton name
          | None -> Bindings.empty in
        this#with_bindings loc ~lexical:true bindings (fun () ->
          run_opt this#function_identifier id;
          this#lambda loc params body;
        ) ();
      end;

      expr
    end

  let program ?(ignore_toplevel=false) program =
    let loc, _, _ = program in
    let walk = new scope_builder in
    let bindings =
      if ignore_toplevel then Bindings.empty
      else
        let hoist = new hoister in
        hoist#eval hoist#program program
    in
    walk#eval (walk#with_bindings loc bindings walk#program) program
end

module With_Loc = Make (Loc_sig.LocS) (Scope_api.With_Loc)
module With_ALoc = Make (Loc_sig.ALocS) (Scope_api.With_ALoc)

include With_Loc
